Field
The present invention relates to a light emitting diode (LED) driving circuit using a double bridge diode and an LED illumination device including the same, and more particularly, to an LED driving circuit using a double bridge diode capable of compensating for an optical output of an LED illumination using an element and/or a circuit in which energy may be charged or from which the energy may be discharged, and an LED illumination device including the same.
Discussion of the Background
Light emitting diodes (LEDs) are generally driven in a direct current (DC) driving scheme. In the case of the DC driving scheme, an alternating current (AC) to DC converter such as a switching mode power supply (SMPS), or the like, is necessarily required. However, this power converter raises a manufacturing cost of an illumination equipment, makes it difficult to miniaturize the illumination equipment, decreases energy efficiency of the illumination equipment, and shortens a lifespan of the illumination equipment due to a short lifespan.
In order to solve these problems of the DC driving scheme, an AC driving scheme of the LEDs has been suggested (in Korean Patent Laid-Open Publication No. 10-2012-0032509, and the like). However, in the case of a circuit according to this technology, a power factor is decreased due to discordance between an input voltage and currents output from the LEDs, and a non-emissive section of the LEDs is long, such that a flicker phenomenon that a user recognizes flickering of an illumination occurs.
In order to solve the problems of the AC driving scheme of the LEDs as described above, a sequential driving scheme of AC LEDs has been suggested (in Korean Patent Laid-Open Publication No. 10-2012-0041093, and the like). According to the sequential driving scheme of the AC LEDs described above, in a situation in which an input voltage is increased over time, a first LED first starts to emit light at Vf1, a second LED connected to the first LED in series starts to emit light at Vf2, which is a voltage higher than Vf1, and a third LED connected to the second LED and the first LED in series starts to emit light at Vf1, which is a voltage higher than Vf2. In addition, in a situation in which the input voltage is decreased over time, the third LED first stops emitting the light at Vf1, the second LED stops emitting the light at Vf2, and the first LED finally stops emitting the light at Vf1, such that an LED driving current is designed so as to be approximate to the input voltage. According to the sequential driving scheme of the AC LEDs described above, an LED driving current converges in a form similar to an AC input voltage, such that a power factor is improved, but a flicker phenomenon in a non-emissive section in which an input voltage does not arrive at Vf1 still occurs, and light emitting times of each LED light emitting module are different from each other, such that optical characteristics of an illumination device are not uniform.
In order to solve the problems of the sequential driving scheme of the AC LEDs as described above, various technologies for removing the non-emissive section using a smoothing capacitor, a power factor correction circuit, and the like, have been suggested (in Korean Patent Laid-Open Publication No. 10-2010-0107196). However, according to these technologies, a total harmonic distortion (THD) is deteriorated due to element characteristics that a current is rapidly increased at a point in time at which the smoothing capacitor starts to be charged. In addition, since the smoothing capacitor should maintain a voltage of at least Vf3 or more in order to drive all the LEDs in the non-emissive section, a high capacitance is required. Further, for this reason, a cost of the smoothing capacitor is increased, and it is difficult to miniaturize an LED illumination equipment. FIG. 1A is a block diagram illustrating a configuration of an LED illumination device including a smoothing capacitor according to the related art, and FIG. 1B is waveform diagrams for describing a voltage waveform of AC power input to the LED illumination device illustrated in FIG. 1A, a current waveform of the AC power, and a waveform of a driving voltage actually applied to an LED group. As illustrated in FIG. 1A, the LED illumination device including a smoothing capacitor according to the related art may be configured to include a rectifying module 10, an LED driving module 20, an LED module 30 including a plurality of LED groups 31 to 34, and the smoothing capacitor Cdc1. The rectifying module 10 includes a full-bridge diode formed by four diodes D1 to D4, and serves to full-wave-rectify an applied AC voltage VAC and output the full-wave-rectified voltage Vrec. The smoothing capacitor Cdc1 is charged or discharged depending on a voltage level of the rectified voltage Vrec to serve to smooth the rectified voltage Vrec. A capacitance of the smoothing capacitor Cdc1 may be variously configured as needed. In the case of the related art illustrated in FIG. 1A, an example in which a capacitance of the smoothing capacitor Cdc1 is selected so that a minimum voltage level of the smoothing capacitor Cdc1 is Vf3 or more so as to drive three LED groups 31 to 33 in the non-emissive section is illustrated. The LED driving module 20 decides a voltage level of an applied driving voltage Vp and controls driving of the plurality of LED groups 31 to 34 depending on a voltage level of the driving voltage Vp. The LED driving module 20 may control driving of four LED groups 31 to 34. However, since the driving voltage Vp input to the LED groups 31 to 34 is maintained at at least Vf3 or more due to the smoothing capacitor Cdc1 as described above, a first LED group driving unit VDR1 and a second LED group driving unit VDR2 each controlling driving of a first LED group 31 and a second LED group 32 are not substantially operated. The LED driving module 20 controls a third LED group driving unit VDR3 or a fourth LED group driving unit VDR4 depending on the voltage level of the driving voltage Vp (a voltage level of a ripple voltage of the smoothing capacitor Cdc1) to perform a control so that the first to third LED groups 31 to 33 or the first to fourth LED groups 31 to 34 emit light. However, in the case of the related art as illustrated in FIG. 1A, an input current IAC of an AC power supply and an LED driving current are completely decoupled from each other by the smoothing capacitor Cdc1, and a light amount and power characteristics of the LED module 30 completely depend on the smoothing capacitor Cdc1. Meanwhile, as illustrated in a waveform diagram of the input current IAC of the AC power supply of FIG. 1B, it may be confirmed that a conduction time (that is, a charging time of the smoothing capacitor Cdc1) (time sections t1 to t3 and t5 to t7) is relatively short, and a magnitude of the input current is large (sharp). Therefore, in the case of the related art as illustrated in FIGS. 1A and 1B, the current IAC input from the AC power supply is not substantially used to drive the LED, and THD and power factor (PF) characteristics are significantly deteriorated, such that it is difficult to apply the related art as illustrated in FIGS. 1A and 1B to a high capacity product.
Meanwhile, in order to solve the problems of the related art as described above, an LED illumination device including a power factor correction circuit such as a valley-fill circuit has been suggested. FIG. 2A is a block diagram illustrating a configuration of an LED illumination device including a valley-fill circuit according to the related art, and FIG. 2B is waveform diagrams for describing a voltage waveform of AC power input to the LED illumination device illustrated in FIG. 2A, a current waveform of the AC power, a waveform of a driving voltage actually applied to an LED group, and an LED driving current. As illustrated in FIG. 2A, the LED illumination device including a valley-fill circuit may be configured to include a rectifying module 10, an LED driving module 20, an LED module 30 including a plurality of LED groups 31 to 34, and the valley-fill circuit 40. Since a description for the rectifying module 10, the LED driving module 20, and the LED module 30 including the plurality of LED groups 31 to 34 is the same as the description provided above with reference to FIG. 1A, a description for an overlapped content will be omitted, and the valley-fill circuit 40 will be mainly described. The valley-fill circuit 40, which is a circuit correcting a power factor, is charged or discharged depending on a voltage level of the rectified voltage Vrec to serve to compensate for the rectified voltage Vrec. Although valley-fill circuits having various capacities may be adopted and used as needed, an example in which a capacity of the valley-fill circuit 40 is selected to drive at least two LED groups 31 and 32 is illustrated in FIGS. 2A and 2B. Therefore, the driving voltage Vp input to the LED groups 31 to 34 is maintained at at least Vf2 or more due the valley-fill circuit 40, the first LED group driving unit VDR1 controlling the driving of the first LED group 31 is not substantially operated. The LED driving module 20 controls the second LED group driving unit VDR2, the third LED group driving unit VDR3, or the fourth LED group driving unit VDR4 depending on a voltage level of the driving voltage Vp to perform a control so that the first and second LED groups 31 and 32, the first to third LED groups 31 to 33, or the first to fourth LED groups 31 to 34 emit the light. In the case of the related art as illustrated in FIG. 2A, as illustrated in a waveform diagram of an input current IAC of AC power of FIG. 2B, the input current IAC input from an AC power supply and energy stored in capacitors C1 and C2 of the valley-fill circuit 40 are used together with each other in order to drive the LED module 30, such that a capacitance of the capacitor may be decreased as compared with the LED illumination device including the smoothing capacitor according to the related art. Further, in PF characteristics, a relatively high value may be maintained as compared with the LED illumination device including the smoothing capacitor according to the related art. However, as illustrated in the waveform diagram of the input current IAC of the AC power supply of FIG. 2B, it may be confirmed that a conduction time (that is, a charging time of the valley-fill circuit 40) (time sections t3 to t4 and t11 to t12) is relatively short, and a magnitude of the input current is large (sharp). Therefore, in the case of the related art as illustrated in FIGS. 2A and 2B, a separate current limiting circuit is required in order to improve THD characteristics, and charging of the valley-fill circuit 40 may be performed only from a point in time at which an input voltage VAC becomes a voltage level (that is, Vf4) at which all of the four LED groups 31 to 34 are driven to a point in time at which the input voltage VAC becomes a maximum.
On the other hand, in order to solve the problems of the related art as described above, a technology of controlling charging and/or discharging an energy charging or discharging unit using an active element such as a metal oxide semiconductor field effect transistor (MOSFET), or the like, has been suggested. However, in the case of this technology, charging or discharging loss is generated due to energy consumed in the active element.